The present invention relates to a double bulb mercury vapor lamp apparatus including cooling and infrared filtering systems.
In photodevelopment applications, lamps are used to cure photosensitive materials such as inks, paints and coatings. In modern web or sheet presses, extremely high speeds of operation require the use of high intensity light sources to provide the requisite rapid curing of photosensitive materials during very short exposure times. Mercury vapor lamps are often used to provide the required high intensity light. However, the use of mercury vapor lamps introduces a number of problems.
Mercury vapor lamps must operate at temperatures exceeding the boiling point of mercury, i.e. 450 degrees Celsius, but below the devitrification temperature of the lamp envelope. Thus, these lamps are generally placed in quartz envelopes. When they are used as lamps for photosensitive applications, the high temperatures generated by the bulbs require elaborate cooling systems to prevent the materials being cured from being damaged by the heat. At the same time, the considerable infrared radiation given off by mercury vapor bulbs can provide unwanted heating of the curing materials as well.
These problems were addressed in U.S. Pat. No. 4,000,407 ('407 patent), which is incorporated herein by reference. In the '407 patent, a quartz envelope mercury vapor bulb is positioned in a reflector housing with water circulated through the housing as a cooling agent. The bulb is positioned within an arc-shaped reflector which directs light from the bulb toward the material being cured. Positioned between the bulb and the curing material are a pair of transparent tubes, which may be made of quartz as well. Water or another transparent cooling medium is circulated through the tubes to provide additional cooling and to act as a filter for infrared radiation generated by the bulb. Thus, the curing material is protected from direct heat generated by the bulb and from indirect heating due to the infrared radiation emitted by the bulb.
While this arrangement has proven to be generally satisfactory, speed advancements in the printing art since the '407 patent issued have necessitated the use of stronger radiation sources with consequent increased cooling requirements, but confined within a housing of comparable size.
It is clear then, that a need exists for an improved mercury vapor lamp apparatus with infrared filtering and cooling systems which can produce enhanced illumination in a photosensitive application without damaging the materials to be cured. Such a lamp must provide the enhanced illumination without producing temperatures or infrared radiation which can damage the curing materials, and must be contained within a housing of comparable size to ones in prior art single bulb lamps.